The present invention relates to a lubrication system for a tool holder, and more particularly relates to improvement in lubrication of a tool holder generally used for vibration cutting such as vibration boring or vibration tapping.
Such vibration cutting is widely known to public and used in real production of various mechanical parts. One example of vibration cutting is disclosed in Japanese Patent Publication Hei 2-7769 issued in 1990.
In vibration cutting, a tool held by a tool holder rotate about its own longitudinal axis whilst concurrently revolving about the primary axis, usually the center axis, of the tool holder. Since the tool is held by a tool holder shaft of the tool holder which is operationally coupled to a drive shaft rotatably mounted to a casing of the tool holder. Thus in operation, the tool holder shaft needs to be driven for vibratory rotation, which is composed of slow rotation about its own longitudinal axis and quick revolution about the primary axis of the tool holder.
More specifically, the drive shaft is rotatably mounted to the tubular easing for rotation about the primary axis and connected at its proximal end to a given drive source. The drive shaft is provided on its distal end with an eccentric pin having a secondary axis deviated from the primary axis. A rotary holder is arranged within the casing surrounding the eccentric pin on the drive shaft for rotation about the primary axis at a speed lower than that of the drive shaft. The rotary holder may be coupled either to the drive shaft via a reduction unit or to a separate drive source of a low speed of rotation. The tool holder shaft is coaxially carried by the rotary holder in an arrangement such that it is able to rotate about its own longitudinal axis while concurrently revolving about the primary axis. A vibration piece is rotatably inserted over the eccentric pin either directly or via a bearing. The vibration piece is provided with a radially extending transmission rod which is received at its outer end in the rotary holder in a longitudinally slidable and laterally rotatable fashion. A transmission bar is slidably coupled to the distal end of the vibration piece and connected to the proximal end of the tool holder shaft at a spot deviated from the primary axis.
As the drive shaft rotates, the vibration pin is driven for a composite movement which is composed of low speed rotation about the secondary axis and high speed revolution about the primary axis. This composite movement of the vibration piece is transmitted, via the transmission bar, to the tool holder shaft to cause the vibratory rotation of the latter.
In the above-described construction, the joint between the eccentric pin and the vibration piece forms the heart of the tool holder and is subjected to the maximum sliding contact. Conventionally, lubrication oil is initially fused into a space in the joint or into a bearing present at the joint and there is no positive supply of lubrication oil to the joint. The initial lubrication of a limited amount cannot endure the maximum sliding contact at the joint over a long period of use. Deterioration in quality of the initial lubrication often accompanied with gradual reduction in quantity tends to cause serious seizure at the joint.